Method of heating plastic pipe

ABSTRACT

An inplace gasket belling machine wherein a plastic pipe is received in a tilt clamp fixture and tilted thereon for receiving a heating bell on one end portion of the pipe. Heated fluid is directed over the inserted pipe end portion. The heating bell may be withdrawn from the pipe in intermittent steps to afford a temperature gradient along the pipe end portion. The pipe is then tilted to a horizontal disposition for the insertion of a gasket belling mandrel into the heated end portion of the pipe. A gasket magazine is supported adjacent the mandrel for automatically placing an annular gasket on the mandrel for insertion into the pipe end portion. The mandrel includes an outer housing and a mandrel body portion telescopically received within the outer housing. The outer housing has a stop shoulder and a gasket positioning sleeve extended forwardly therefrom. The mandrel body portion has a flared pipe expanding portion and a gasket carrying portion rearwardly thereof. Upon insertion of the flared portion into the heated end of the pipe, the outer housing collapses onto the mandrel body portion for precise positioning of the gasket within the pipe end portion. Upon withdrawal of the gasket positioning sleeve from said pipe end portion, the pipe end portion is collapsed by vacuum means onto the mandrel body portion and cooled prior to withdrawal of the mandrel body portion from the belled pipe end portion.

This application is a divisional application from co-pending parentapplication Ser. No. 902,443, filed May 3, 1978.

BACKGROUND OF THE INVENTION

This invention relates to improvements in an inplace gasket bellingmachine and more particularly to improved means for supporting a pipe inthe machine, improved means for heating one end portion of the pipe, animproved belling mandrel and means for automatically placing a gasket onthe belling mandrel.

Presently known inplace gasket belling machines have severalshortcomings which are resolved by the improvements of the presentinvention. Generally, the pipe end portion to be belled is heated bystanding the pipe on end and immersing the end portion into a bath ofheated fluid. Problems associated with this method of heating are first,that substantial vertical clearance is required for standing the pipeson end and second, that the entire end portion of the pipe is heated toa generally uniform temperature so that a substantial temperatureinterface is formed between the immersed and non-immersed portions. Thesudden temperature change along the pipe increases the chances of theend portion being axially collapsed during insertion of the bellingmandrel.

A related problem associated with the immersion type heating of the pipeend portion is that somewhat complex pipe handling apparatus has beenrequired for supporting the pipe in perpendicularly related heating andbelling positions.

It has generally been the practice to manually place gaskets on thebelling mandrel in order to provide clearance for passage of the mandrelinto the heated end portion of a pipe. This operation thus necessitatesoperator assistance with the belling of each pipe.

Conventional inplace gasket belling machines have heretofore employed afixed mandrel and a single speed drive means for advancing the mandrelinto one end of a pipe. The speed of the drive means is generally acompromise between a relatively fast speed conducive to expanding thepipe end portion and a slow speed conducive to accurate depth control ofthe mandrel within the pipe. Furthermore, it has been necessary toprovide independent drive means for a gasket positioning sleeve on themandrel because of the required axial movement of the sleeve relative tothe mandrel during the belling operation.

It is believed that all of the above-mentioned shortcomings are resolvedby the improved inplace gasket belling machine of the present invention.

SUMMARY OF THE INVENTION

The inplace gasket belling machine of the invention includes an axiallymovable belling mandrel and a heating bell movably supported adjacentthe mandrel at an inclination to the axis of the mandrel. The pipe to bebelled is supported on a simple tilt clamp fixture which may be tiltedan acute angle for movement of the pipe between a heating position inalignment with the heating bell and a belling position in alignment withthe belling mandrel. A pipe clamp on the fixture securely holds a pipeduring both the heating and belling operations and opens for releasing afinished pipe and receiving another pipe to be belled.

The heating bell of the invention includes means for advancing the bellonto one end portion of a pipe supported in the heating positiontherefor. By withdrawing the heating bell from the pipe end portion inselected intermittent steps, a temperature gradient may be set up in thepipe end portion. Accordingly, the tip of the pipe may be heated to apredetermined temperature substantially higher than the innermost end ofsaid pipe end portion. The temperature interface between the heated andnon-heated portions of the pipe is thus minimized thereby improving thestructural integrity of the pipe during the belling operation. Since theheating bell is inclined at an acute angle to the axis of the bellingmandrel, the pipe need be inclined only an acute angle for movementbetween the heating and belling positions therefor. As a result, littleif any vertical clearance is required above the height of the machine.

The present invention also includes a gasket magazine for sequentiallydispensing annular gaskets to a gasket holding ring situated in the pathof the mandrel for automatic placement of a gasket onto the mandrel. Thegasket holding ring includes opposite side portions which areautomatically laterally separated to provide free passage of the mandreltherebetween. Since both the gasket magazine and gasket holding ring areoperatively controlled by movement of the mandrel, no separate drivemeans is required for these members nor is operator assistance requiredfor the belling operation other than to occasionally replenish thesupply of gaskets within the magazine.

The belling mandrel of the invention includes a mandrel body portiontelescopically received within an outer housing. The body portionincludes means for radially expanding the pipe and for carrying thegasket into the pipe end portion. The outer housing includes a stopshoulder and a gasket positioning sleeve extended forwardly therefromfor accurately positioning the gasket within the pipe end portion whenthe stop shoulder is advanced to engage the end of the pipe. A springwhich biases the body portion forwardly of the outer portion permits thebody portion to be retained within the pipe while the gasket positioningsleeve is withdrawn therefrom so that the expanded end portion of thepipe may be collapsed onto the body portion by vacuum means prior towithdrawal of the body portion from the pipe. A single drive cylinderthus controls the movement of both telescoping portions of the mandrel.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will become apparent uponreading the following detailed description and upon reference to thedrawings, in which:

FIG. 1 is a foreshortened side elevational view of the inplace gasketbelling machine;

FIG. 2 is a front sectional view of the machine taken along line 2--2 inFIG. 1;

FIG. 3 is a detail side elevational view showing the heating belladvanced onto an end portion of a downwardly tilted pipe supported inthe tilt clamp fixture;

FIG. 4 is an enlarged side sectional view of the heating bell with apipe end portion received therein;

FIG. 5 is an enlarged detail perspective view of the gasket holdingring;

FIG. 6 is a top partially sectional view taken along line 6--6 in FIG. 1showing the gasket holding ring disposed within the path of the mandrel;

FIG. 7 is a top partially sectional view, similar to FIG. 6, but showingthe mandrel advanced for receiving a gasket from the gasket holdingring;

FIG. 8 is top partially sectional view, similar to FIG. 7, but showingthe mandrel further advanced for carrying the gasket forwardly of thegasket holding ring;

FIG. 9 is side sectional view, taken along line 9--9 in FIG. 8, showingthe internal construction of the mandrel;

FIG. 10 is a detail side sectional view of a forward portion of themandrel showing the radially expanded segments for expanding the pipe toreceive a gasket;

FIG. 11 is a top partially sectional view, similar to FIG. 8, showingthe outer portion of the mandrel fully advanced into engagement with theend of the pipe;

FIG. 12 is a side sectional view, taken along line 12--12 in FIG. 11;

FIG. 13 is a side sectional view of the mandrel, similar to FIG. 12, butshowing a gasket positioning sleeve axially withdrawn from the pipe endportion; and

FIG. 14 is a side sectional view of a completed belled end portion of apipe shown in mating engagement with the opposite end of a second pipe.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The inplace gasket belling machine, indicated generally at 10 in FIG. 1,includes an elongated main frame 12 and a tilt clamp fixture 14 at oneend of the frame for receiving and securely holding a pipe to be belled.

The tilt clamp fixture 14 includes an elongated tilt bar 16 pivotallysupported intermediate its ends on a stub shaft 18 carried between apair of upstanding brackets 20 on the main frame 12. The tilt bar has agenerally saddle shaped upstanding pipe support bracket 22 at one endand a pipe clamp 24 at the other end for cooperatively securely holdinga pipe relative to the tilt bar 16. A hydraulic cylinder 26 is pivotallyconnected between the tilt bar 16 and main frame 12 for pivotally movingthe tilt bar between the belling position shown in FIG. 1 and theheating position shown in FIG. 3, as will be further describedhereinbelow.

The pipe clamp 24, shown best in FIGS. 1 and 2, has a pair of arcuateclamp jaws or arms 28 interconnected for pivotal movement about a commonlongitudinally extended clamp pin 30. The clamp pin pivotally supportsthe arms 28 on an upstanding frame 32 rigidly connected to the rearwardend of the tilt bar 16. The clamp arms 28 have semi-cylindrical clampingsurfaces 34 adapted to be closed in clamping relation against oppositesides of a pipe 36, as shown in FIG. 2. The clamp arms 28 are pivotallymoved in unison by a toggle mechanism including a pair of pivot links 38and 40 which are pivotally connected to one end of a hydraulic cylinderunit 42 carried on the frame 32. Thus the clamp arms 28 are closed inresponse to extension of the hydraulic cylinder unit 42 and opened inresponse to retraction of the cylinder unit 42.

To deliver a pipe to the tilt clamp fixture 14, an automatic beller feedassembly is provided, as shown in FIG. 2. A downwardly inclined pipedelivery rack 46 is supported laterally of the tilt clamp fixture 14. Atipping trough 48 is pivotally connected to the outer edge of the rack46 and positioned for receiving a pipe 36 from an extruding machine (notshown). After opening the clamp arms 28 of the pipe clamp 24, ahydraulic cylinder unit 50 may be extended to pivot trough 48 upwardlyto allow the pipe 36 to roll down the rack 46 and into the pipe clamp 24and saddle bracket 22. Likewise, to discharge a pipe from the tilt clampfixture 14 upon completion of the belling operation, the pipe clamp 24is again opened allowing the finished pipe to roll away from the fixtureon a discharge ramp 52 as indicated by arrow 54 in FIG. 2.

To heat the pipe end portion 58 which is to be belled, there is provideda heating bell 60 supported on the main frame 12 rearwardly of and belowthe pipe clamp 24 in its elevated pipe receiving position. Referring toFIGS. 1 and 3, it is seen that the heating bell 60 is supported on oneend of a hydraulic cylinder unit 62 for movement between retractedposition shown in FIG. 1 and the extended heating position shown in FIG.3. It is seen in FIG. 3 that when the tilt clamp fixture 14 is tilted tothe heating position therefor, the pipe 36 is axially aligned with theheating bell 60 for movement of the heating bell onto and around thepipe end portion 58. Heating bell 60 is a generally cup-shaped memberhaving a generally cylindrical sidewall 64, a closed rear wall 66 and anopen end 68. A hinged cover 70 is adapted to close the open end 68 inthe retracted position of the heating bell (FIG. 1) to prevent the entryof dirt or other matter therein.

Referring to FIG. 4, it is seen that the sidewall 64 includes a pair ofgenerally cylindrical wall portions 72 and 74 arranged one within theother such that a generally cylindrical space 76 is formed therebetween.Space 76 is of a diameter for receiving the pipe end portion 58 asshown.

To heat the pipe end portion 58 within the heating bell 60, preheatedfluid is pumped through a main supply conduit 78 and throughcircumferentially spaced inner and outer supply conduits 80 and 82 whichcommunicated with openings at the forward ends of the wall portions 72and 74 for circulating the heating fluid over the inside and outsidesurfaces of the pipe end portion 58. A drain conduit 84 communicateswith the lowermost corner of the heating bell 60 for returning theheating fluid to a reservoir (not shown). A pair of annular seals 86 and88 close the open end of cylindrical space 76 to prevent the flow ofheating fluid outwardly therethrough. The seals also serve to clean thefluid from the pipe end portion as the heating bell 60 is withdrawnaxially from the pipe. Fluid which does pass forwardly of the sealsdrains through a conduit 90 to a separate tank (not shown).

A preferred fluid to be circulated through the heating bell is glycerinpreheated to a temperature of about 320° F.

It can be seen in FIG. 3 that by withdrawing the heating bell 60 fromthe pipe end portion 58 in selected intermittent steps, the rearward end90 of the pipe will be heated for a longer duration than the upstreamend 91 of the pipe end portion 58. Thus the temperature of the end ofthe pipe may be precisely controlled and maintained at a substantiallyhigher temperature than the upstream portion 91. A temperature gradientis thus created along the pipe end portion 58.

Once the heating bell 60 is completely withdrawn from the pipe endportion 58, the tilt bar 16 is pivoted to the belling position thereforas shown in FIG. 1 wherein the pipe 36 is disposed in axial alignmentwith a belling mandrel 92 carried on the rearward end of the main frame12. The mandrel 92 is axially aligned with and supported on the forwardend of a piston 94 of a mandrel cylinder unit 96. Thus actuation of thecylinder unit 96 is effective to move the mandrel 92 longitudinallytoward and away from the pipe end portion 58.

Referring to FIGS. 6 and 9, it can be seen that the mandrel 92 includesa generally cylindrical outer housing 98 having a rear closure portion100 bolted thereto. A front cover plate 102 on outer housing 98 has acentral opening therethrough defined by a forwardly extended stop sleeve104 and a gasket positioning sleeve 106 extended forwardly from stopsleeve 104. The gasket positioning sleeve 106 is of a lesser outsidediameter than the stop sleeve 104 to define a radially extended stopshoulder 108 at the juncture therebetween.

Telescopically received within the mandrel outer housing 98 is a mandrelbody portion 110 including a forwardly extended cylindrical portion 112slidably supported within the gasket positioning sleeve 106. Rearwardlyof the cylindrical portion 112, the body portion 110 has a radiallydirected annular surface 114 engageable with the front cover plate 102to define a forward limit position for the body portion relative to saidouter housing. A rearward limit position for said body portion 110 isdefined by engagement of the rearward end 116 of the body portion 110with the rear closure portion 100 of outer housing 98. A spring 118 isarranged in compression between the body portion 110 and rear closureportion 100 to urge the body portion toward the forward limit positiontherefor.

Referring again to FIGS. 6 and 9, a nose member 120 is secured to thefront end of the mandrel body portion 110 by a bolt 122. The nose member120 is generally cylindrical with an outer diameter approximately equalto the inner diameter of a pipe to be belled. A forwardly and inwardlytapered frustoconical surface 124 on the forward end of the nose member120 serves to guide the mandrel into the end of a pipe to be belled.

Rearwardly of the nose member 120 the mandrel body portion 110 includesa rearwardly and outwardly flared pipe expanding portion 126 which willbe further described hereinbelow. Rearwardly of the flared portion 126,the mandrel body portion 110 includes a recessed or radially depressedgasket carrying portion 128. The depressed diameter of the gasketcarrying portion 128 is adapted to accommodate an inwardly extendedflange 130 on a gasket 132 as shown in cross section in FIG. 9, so thatthe generally cylindrical inside surface 134 of the gasket is generallycontinuous with the outside diameter of the mandrel body portion 110rearwardly thereof. Gasket 132 has an arcuate outer surface withadditional outwardly and rearwardly extended annular flanges 134 and 136respectively.

To automatically place a gasket 132 onto the mandrel 92, there isprovided a gasket magazine 138 (FIG. 1) supported on the main frame 12above the mandrel 92 and a gasket holding ring 140 supported in the pathof the mandrel 92 and adapted for receiving a gasket from the magazine138.

The gasket magazine 138 includes an elongated housing 142 as shown inFIGS. 1 and 2, said housing having closed sidewalls 144, and a generallycontinuous top wall 146, bottom wall 148 and opposite end walls 150 and152. A conveyor means is trained about a pair of longitudinallyspaced-apart transverse rollers 154 and 156 extended transverselythrough the housing 142. The conveyor means carries a plurality ofspaced-apart support members 158 directed perpendicularly to theconveyor means for defining gasket-receiving compartments 160 betweenthe support members. The bottom wall 48 is provided with an opening at162 above the gasket holding ring 140. When the conveyor means isadvanced to register a compartment 160 with the opening 162, a gasket isdispensed from the compartment through the opening by gravity and intothe gasket holding ring 140.

Coacting means is provided on the gasket magazine 138 and mandrel 92 forautomatically advancing the conveyor means by one compartment inresponse to rearward movement of the mandrel to its retracted positionshown in FIG. 1. The coacting means includes a rock arm 164 pivotallyconnected to roller 156 by a one-way clutch 166 for rotating the roller156 in response to clockwise pivotal movement of the rock arm 164 asseen in FIG. 1. A depending lever 168 is pivotally connected to thehousing 142 at 170. A linkage 172 interconnects the rock arm 164 andlever 168 for pivotal movement in unison. The lower end of lever 168extends downwardly into the path of the mandrel 92 such that rearwardmovement of the mandrel causes the outer housing 98 to abutt against thelower end of lever 168 to pivot the same in a clockwise direction inresponse to rearward movement of the mandrel 92.

The gasket dispensed from the magazine 138 is received within the gasketholding ring 140 shown in FIG. 5. Ring 140 includes separable sideportions 174 and 176 which, when engaged, define a vertical gasketreceiving slot 178 adapted for receiving a gasket from the magazine andsupporting the gasket in registration with a central opening 180 adaptedfor receiving the forward portion of the mandrel 92 as it is advancedforwardly toward the pipe 36.

The ring side portions 174 and 176 are supported on the forward ends ofrespective elongated support arms 182 and 184, the rearward ends ofwhich are pivotally supported relative to the main frame 12 aboutupright axes 186 and 188 respectively on opposite sides of the mandrel92. The support arms include inwardly converging medial portions 190 and192 and elongated cam slots 194 and 196.

The outer housing 98 of the mandrel carries a pair of upright cam pins198 and 200 in laterally spaced relation therefrom for receipt withinthe cam slots of the support arms. It can be seen in FIG. 7 that the campins engage the inwardly converging medial portions of the cam slots atthe time the gasket holding ring 140 is registered with the gasketcarrying portion 128 of the mandrel. It can be seen in FIG. 8 thatcontinued forward advancement of the mandrel pivots the support arms 182and 184 outwardly to separate the side portions 174 and 176 of thegasket holding ring for passage of the mandrel between the separatedside portions. Likewise, the coacting cam pins 198 and 200 and cam slots194 and 196 are effective to re-engage the gasket holding ring sideportions together in response to rearward movement of the mandrel to itsretracted position of FIG. 6.

It can be seen in FIG. 7 that as the mandrel is advanced through thegasket holding ring 140, the flared portion 126 of the mandrel issimultaneously advanced into the heated end portion 58 of the pipe toradially expand the same. Note that forward advancement of the mandrelis controlled by the mandrel cylinder unit 96 and that the mandrel bodyportion 110 begins to telescope into the outer housing 98 at the pointof initial contact of the mandrel with the end of the pipe.

Referring to FIGS. 9 and 10, the flared portion 126 of the mandrelincludes three circumferentially spaced segments 202 rockably secured attheir forward ends between the front of the mandrel and the nose member120 for movement of the rear ends radially of the mandrel. Each segmentor jaw 202 has a hemispherical cam member 204 welded to its inner side.The segments 202 are expanded by forward axial movement of a cone shapedcam member 206 between the hemispherical cam members 204. The coneshaped cam member is secured to the forward end of a cylindrical drivemember 208 secured to the piston of a hydraulic cylinder unit 210supported within the mandrel body portion 110. Accordingly, the segments202 are radially expanded in response to extension of hydraulic cylinder210 and they are free to collapse radially in response to retracttion ofcylinder 210 to the position shown in FIG. 9. It can be seen that thehydraulic lines 212 extend outwardly of the mandrel body portion 110through an elongated slot 214 in the mandrel outer housing 98 toaccommodate relative telescoping movement between the mandrel portions.

Vacuum means associated with the mandrel body portion 110 for a purposedescribed hereinbelow includes a vacuum tube 216 inserted through asecond elongated slot 218 in outer housing 98 and through the mandrelbody portion for communication with the interior thereof. A plurality ofcircumferentially spaced openings 220 are formed through the rearwardend of the mandrel gasket carrying portion 128. The interior of themandrel body portion 110 thus forms a vacuum chamber sealed at theforward end by an annular seal 222 carried on drive member 208 andsealed at the other end by the rear wall on which the cylinder 210 ismounted. An annular clearance is provided between the forward end of thecylinder 210 and rearward end of the mandrel cylindrical portion 112 toprovide communication between the vacuum openings 220 and vacuum tube216.

The operation of the inplace gasket belling machine is as follows.Hydraulic cylinder 50 is first actuated for raising the tipping trough48 to deliver a pipe to the tilt clamp fixture 14. The pipe is receivedin the open clamp arms 28 of pipe clamp 24 and onto the saddle bracket22. Upon extension of hydraulic cylinder 26, the pipe clamp is closedand hydraulic cylinder 26 is extended to tilt the pipe approximately 15°to the heating position shown in FIG. 3. The heating bell cylinder 60 isthen extended to advance the heating bell onto the pipe end portion 58.Heated glycerin is pumped through the heating bell and the hydrauliccylinder 62 is retracted in intermittent steps for precision steppedheating of the pipe end portion 58. When the heating bell 60 iswithdrawn clear of the pipe, the tilt bar 16 is pivoted to move the pipeto the belling position therefor shown in FIG. 1 in axial alignment withthe belling mandrel 92.

Belling of the heated end portion of the pipe is initiated by extensionof the mandrel cylinder 96 whereupon the mandrel is advanced from theretracted position of FIG. 6 to the position of FIG. 7 into and throughthe gasket holding ring 140 for receiving a gasket onto the gasketcarrying portion 128. At this point the mandrel flared portion 126, withits expandable segments 202 collapsed, is being advanced into the heatedend portion of the pipe and the mandrel body portion 110 has begun totelescope into the outer housing 98.

Continued forward advancement of the outer housing 98 is effective tolaterally separate the side portions 174 and 176 of the gasket holdingring 140 by the coaction of the cam pins 198, 200 in the cam slots ofthe support arms 182, 184. As the gasket 132 approaches the end of thepipe, FIGS. 8 and 9, a limit switch (not shown) energizes a solenoid toinitiate the extension of hydraulic cylinder 210 within the body portion110. As shown in FIG. 10, the cone shaped cam 206 is advanced betweenthe hemisperhical cam members 204 to radially expand the segments 202 toenable insertion of the gasket 132 into the end of the pipe. Preferably,the pipe is not expanded so much that clearance is provided between thegasket and pipe, but only enough to allow insertion of the gasketwithout catching on the end of the pipe. The pliability of the end ofthe pipe due to heating facilitates such expansion.

Upon continued advancement of the mandrel, the increased frictionbetween the mandrel flared portion 126 and cooler portions of the pipecauses the mandrel body portion 110 to be fully telescoped to itsrearward limit position of FIG. 12 against the urging of spring 118.Advancement of the mandrel stops when the stop shoulder 108 engages theend of the pipe. At this point, the gasket positioning sleeve 106 is incontact with the gasket 132 to assure its fixed position relative to thepipe end and to assure that it is clear of the vacuum openings 220.Another limit switch initiates the retraction of hydraulic cylinder 210to permit the expanding segments 202 to collapse within the pipe endportion.

Referring to FIG. 13, it is seen that initial retracting movement of themandrel cylinder effects a withdrawal of only the outer housing 98 towithdraw the gasket positioning sleeve 106 from the end of the pipe. Atthe same time, the mandrel body portion remains stationary within thebelled end of the pipe due to relative telescoping movement between theouter housing 98 and body portion 110 under the urging of spring 118. Avacuum is then applied to the interior of the body portion by the vacuumtube 216 to collapse the heated belled portion of the pipe onto themandrel. Next, the collapsed belled end of the pipe is showered withcool water from hose means indicated at 224 to cool the pipe from about300° F. down to approximately room temperature. Since at this point, themandrel body portion 110 has attained its forward limit position withinthe outer housing 98, further retraction of the mandrel cylinder 96 iseffective to withdraw both portions of the mandrel in unison from thebelled end of the pipe.

Retraction of the mandrel causes the separated side portions 174 and 176of the gasket holding ring 140 to converge together for receivinganother gasket from the magazine 138. It is seen in FIG. 1 thatretraction of the mandrel forces the outer housing 98 against dependinglever 168 which pivots rock arm 164 clockwise to advance anothermagazine compartment 160 into registration with the opening 162 fordispensing a gasket into the holding ring 140. Finally, the pipe clamp24 of the tilt clamp fixture 14 is opened for releasing the completedpipe onto the discharge ramp 52 and for receiving another pipe from ramp46.

It is preferred that the mandrel cylinder 96 be adapted for variablespeed operation so that the mandrel may be advanced slowly through thegasket holding ring 140 for receiving a gasket, afterwhich the mandrelis accelerated to facilitate flaring of the pipe and insertion of thegasket 132 into the end of the pipe without obstruction. Once the gasketis within the pipe end portion, the mandrel is again slowed forprecision control of the depth of advancement into the pipe. A two-speedmandrel has been found satisfactory for this purpose.

It will be apparent that there has been described herein novel methodsof heating and belling one end portion of a pipe independently of thespecific apparatus shown and described.

What is claimed is:
 1. A method of heating one end portion of a plasticpipe comprising:providing a heating bell having a generally continuoussidewall and an open end for receiving said pipe end portiontherethrough, advancing one of said pipe and heating bell toward theother whereby said pipe end portion is axially inserted through saidopen end and received within said sidewall, directing a flow of heatingfluid over the inserted pipe end portion, and withdrawing said one ofsaid pipe and heating bell away from the other for removal of the heatedpipe end portion from the heating bell, said withdrawing step includingremoving said pipe end portion from said heating bell in selectedintermittent steps for step heating of said pipe end portion.
 2. Themethod of claim 1 wherein said withdrawing step includes partiallyremoving the inserted pipe end portion from said heatingbell,continuously directing heating fluid onto said inserted pipe endportion to effect a temperature gradient therein, and removing theremainder of said pipe end portion from said heating bell.
 3. The methodof claim 1 including,tilting said heating bell so as to position saidopen end above the opposite end thereof, moving said pipe to a heatingposition in alignment with said heating bell, maintaining said pipe insaid heating position, said advancing step including advancing saidheating bell toward and around said pipe end portion, and saidwithdrawing step including withdrawing said heating bell away from saidpipe.
 4. The method of claim 1 wherein said directing step includesdirecting a flow of heating liquid over both the inner and outersurfaces of said inserted pipe end portion.
 5. The method of claim 4wherein said heating liquid is glycerin and further comprisingpreheating said glycerin to a temperature of between 250 and 350 degreesFahrenheit.